Intel X5472 Data Sheet - Page 102
for the Stop Clock State Machine for supported P
UPC - 735858201551
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Features Enhanced Intel SpeedStep Technology creates processor performance states (P-states) or voltage/frequency operating points which are lower power capability states within the Normal state (see Figure 7-1 for the Stop Clock State Machine for supported Pstates). Enhanced Intel SpeedStep Technology enables real-time dynamic switching between frequency and voltage points. It alters the performance of the processor by changing the bus to core frequency ratio and voltage. This allows the processor to run at different core frequencies and voltages to best serve the performance and power requirements of the processor and system. The Quad-Core Intel® Xeon® Processor 5400 Series has hardware logic that coordinates the requested voltage (VID) between the processor cores. The highest voltage that is requested for either of the processor cores is selected for that processor package. Note that the front side bus is not altered; only the internal core frequency is changed. In order to run at reduced power consumption, the voltage is altered in step with the bus ratio. The following are key features of Enhanced Intel SpeedStep Technology: • Multiple voltage/frequency operating points provide optimal performance at reduced power consumption. • Voltage/frequency selection is software controlled by writing to processor MSR's (Model Specific Registers), thus eliminating chipset dependency. - If the target frequency is higher than the current frequency, VCC is incremented in steps (+12.5 mV) by placing a new value on the VID signals and the processor shifts to the new frequency. Note that the top frequency for the processor can not be exceeded. - If the target frequency is lower than the current frequency, the processor shifts to the new frequency and VCC is then decremented in steps (-12.5 mV) by changing the target VID through the VID signals. § 102